Generally, there is no method for judging whether a four-way valve is failed in an existing heat pump water heater system. If the four-way valve is failed, a refrigeration is performed and low-temperature water in a water tank may freeze, such that water inlet of the water tank may be blocked due to ice blockage, thus seriously affecting a usage of a user.
In some cases, the heat pump water heater in related arts may judge whether the four-way valve is failed by determining a difference between temperature of a heat exchanger and environment temperature. In most instances, this solution is feasible; but in a low temperature condition and a condition of low-temperature water, this solution is failed, i.e., the solution cannot be used to judge whether the four-way valve is failed, or in some cases a misjudgment may occur when using this solution.